1. Open "_common_data/clustal/gap_column.aln".
2. MSA sequence area context menu -> Edit -> Remove columns of gaps.
3. Choose "Remove all gap-only columns".
4. Click "Remove".
UGENE 1.16-dev: it take ~15 minutes to remove gaps.
UGENE 1.15.1: it takes ~5 seconds to remove gaps.
Fix the performance problem.
This problem is a blocker because removing of gap columns is used in Sanger alignment feature - one of the main features of UGENE 1.16.